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A matrix-element-based modification of the parton shower

Gabriela Miu

TL;DR

The paper tackles the challenge of accurately describing the W boson transverse momentum distribution across the full pT range by combining matrix-element (ME) corrections with a parton-shower (PS) framework. It modifies the PS for the leading qq'→W process by incorporating ME structures from qqbar'→gW and qg→q'W, and splits the PS into two ME-informed components with a careful mapping between ME and PS variables. By increasing the maximum shower virtuality and embedding the ME correction ratio into the Sudakov evolution, the approach yields good agreement with ME predictions and with D0 data at sqrt(s)=1800 GeV. The results suggest a practical path to extend PS accuracy to large pT without full higher-order calculations and point to applications to Z production and future LHC pp collisions.

Abstract

The transverse momentum distribution of W+/- bosons at hadron colliders is well described by a parton-shower model for small pT values, but not for large ones. This article is an attempt to give a better description of the distribution by using corrections derived from the matrix-element formalism. The parton shower for qqbar->W+/- has been modified to resemble the matrix elements of qqbar->gW and qg->q'W at large pT values. Comparisons between different approaches are presented at sqrt{s}=1800 GeV. The results are also compared with experimental data from the D0 collaboration at Fermilab.

A matrix-element-based modification of the parton shower

TL;DR

The paper tackles the challenge of accurately describing the W boson transverse momentum distribution across the full pT range by combining matrix-element (ME) corrections with a parton-shower (PS) framework. It modifies the PS for the leading qq'→W process by incorporating ME structures from qqbar'→gW and qg→q'W, and splits the PS into two ME-informed components with a careful mapping between ME and PS variables. By increasing the maximum shower virtuality and embedding the ME correction ratio into the Sudakov evolution, the approach yields good agreement with ME predictions and with D0 data at sqrt(s)=1800 GeV. The results suggest a practical path to extend PS accuracy to large pT without full higher-order calculations and point to applications to Z production and future LHC pp collisions.

Abstract

The transverse momentum distribution of W+/- bosons at hadron colliders is well described by a parton-shower model for small pT values, but not for large ones. This article is an attempt to give a better description of the distribution by using corrections derived from the matrix-element formalism. The parton shower for qqbar->W+/- has been modified to resemble the matrix elements of qqbar->gW and qg->q'W at large pT values. Comparisons between different approaches are presented at sqrt{s}=1800 GeV. The results are also compared with experimental data from the D0 collaboration at Fermilab.

Paper Structure

This paper contains 11 sections, 35 equations, 16 figures.

Table of Contents

  1. Introduction
  2. Theory
  3. Mandelstam variables
  4. Matrix elements versus parton showers
  5. Cross sections for $\mathrm{W}$ production
  6. Backwards Evolution
  7. Modeling the parton shower according to the matrix element
  8. Comparing the ME and PS differential cross sections
  9. Description of the modeling
  10. Results
  11. Summary and Outlook

Figures (16)

  • Figure 1: The process $A+B\rightarrow C+D$. The circled region marks the corresponding subprocess $a+b\rightarrow c+d$.
  • Figure 2: The basic QCD branchings
  • Figure 3: The sharing of the momentum fractions $x'$, $x$ and $z$.
  • Figure 4: $\mathrm{q}\mathrm{\overline{q}}' \rightarrow \mathrm{W}$.
  • Figure 5: $\mathrm{q}\mathrm{\overline{q}}'\rightarrow \mathrm{gW}$
  • ...and 11 more figures